Method and apparatus for power device with multiple doped regions

ABSTRACT

A semiconductor device is provided. The device includes a substrate having a first conductivity type. The device further includes a drain region, a source region, and a well region disposed in the substrate. The well region is disposed between the drain region and the source region and having a second conductivity type opposite to the first conductivity type. The device further includes a plurality of doped regions disposed within the well region. The doped regions are vertically and horizontally offset from each other. Each of the doped regions includes a lower portion having the first conductivity type, and an upper portion stacked on the lower region and having the second conductivity type.

FIELD

Example embodiments relate to a semiconductor device, and in particular,to a semiconductor device for a power device with multiple doped regionsand a method for manufacturing the same.

BACKGROUND

Power semiconductor devices for high-voltage applications often usevertical double-diffused metal-oxide-semiconductor field effecttransistors (VDMOSFETs) or laterally diffused metal-oxide-semiconductorfield effect transistors (LDMOSFETs). In order to increase the breakdownvoltage of high-voltage semiconductor devices, several methods arecommonly in use, for example: the doping concentration of a deep wellregion (or known as drift region in the art) is reduced, the depth ofthe drift region is increased, or the length of an isolation structure(or known as field oxide layer in the art) underlying a gate isincreased.

However, when the breakdown voltage of a power semiconductor device isincreased by the above-described ways, the resistance in the ON state(ON-resistance) or the size of the transistor is increased as well,which undesirably reduces the performance of the device or increases thedevice area of a semiconductor device.

Thus, there exists a need in the art for development of a semiconductordevice, capable of increasing the breakdown voltage while preventing theON-resistance or device size from increasing.

SUMMARY OF EMBODIMENTS

Consistent with this disclosure, a semiconductor device is provided. Thedevice includes a substrate having a first conductivity type. The devicefurther includes a drain region, a source region, and a well regiondisposed in the substrate. The well region is disposed between the drainregion and the source region and having a second conductivity typeopposite to the first conductivity type. The device further includes aplurality of doped regions disposed in the well region. The dopedregions are vertically and horizontally offset from each other. Each ofthe doped regions includes a lower portion having the first conductivitytype, and an upper portion stacked on the lower region and having thesecond conductivity type.

Consistent with the disclosure, a semiconductor device is provided. Thedevice includes a substrate having a first conductivity type, and anepitaxial structure having the first conductivity type disposed on thesubstrate. The device further includes a drain region and a sourceregion disposed in the epitaxial structure, and a well region interposedbetween the drain region and the source region. The well region isdisposed in both the substrate and the epitaxial structure, and has asecond conductivity type opposite to the first conductivity type. Thedevice further includes a first doped region disposed in the well regionof the substrate, and a second doped region disposed in the well regionof the epitaxial structure. The first doped region and the second dopedregion are vertically and horizontally offset from each other. Each ofthe doped regions includes a lower portion having the first conductivitytype, and an upper portion stacked on the lower region and having thesecond conductivity type.

Consistent with the disclosure, a semiconductor device is provided. Thedevice includes a substrate having a first conductivity type, and aplurality of epitaxial layers having the first conductivity type anddisposed on the substrate. The device further includes a drain regionand a source region disposed in the uppermost epitaxial layer, and awell region interposed between the drain region and the source region.The well region is disposed in the substrate and the epitaxial layers,and has a second conductivity type opposite to the first conductivitytype. The Device further includes a plurality of doped regions disposedin the epitaxial layers. At least two of the doped regions beingvertically and horizontally offset from each other. Each of the dopedregions includes a lower portion having the first conductivity type, andan upper portion stacked on the lower region and having the secondconductivity type.

Consistent with the disclosure, a method of manufacturing asemiconductor device is provided. The method includes preparing asubstrate of a first conductivity type, and forming a well region in asubstrate. The well region has a second conductivity type opposite tothe first conductivity type. The method further includes forming a masklayer over the substrate. The mask layer includes a plurality of holeshaving different depths from an upper surface of the mask layer. Themethod further includes implanting a first implant, through the masklayer, into the well region to form a plurality of first doped portions.At least two of the first doped portions are vertically and horizontallyoffset from each other. The first doped portions have the firstconductivity type. The method further includes implanting a secondimplant, through the mask layer, into the well region to form aplurality of second doped portions. At least two of the second dopedportions are vertically and horizontally offset from each other. Thesecond doped portions are stacked on the first doped portions and havethe second conductivity type.

Consistent with the disclosure, a method of manufacturing asemiconductor device is provided. The method includes preparing asubstrate of a first conductivity type and forming a well region in thesubstrate. The well region has a second conductivity type opposite tothe first conductivity type. The method further includes forming a firstmask layer over the substrate. The first mask layer including a firsthole. The method further includes implanting a first implant and asecond implant, through the first mask layer, into the well region toform a first doped region. The first doped region includes a lowerportion having the first conductivity type, and an upper portion stackedon the lower region and having the second conductivity type. The methodfurther includes removing the first mask layer from the substrate, andforming a second mask layer over the substrate. The second mask layerincludes a second hole. The method further includes implanting the firstimplant and the second dopant, through the second mask layer, into thewell region to form a second doped region such that the first dopedregion and the second doped region are vertically and horizontallyoffset from each other. The second doped region includes a lower portionhaving the first conductivity type, and an upper portion stacked on thelower region and having the second conductivity type. The method furtherincludes removing the second mask layer from the substrate.

Consistent with the disclosure, a method of manufacturing asemiconductor device is provided. The method includes preparing asubstrate of a first conductivity type, and forming a first well regionin a substrate. The first well region has a second conductivity typeopposite to the first conductivity type. The method further includesforming a first epitaxial layer of the first conductivity type on thesubstrate, and forming a second well region in the first epitaxiallayer. The second well region has the second conductivity type. Themethod further includes forming a first mask layer over the firstepitaxial layer. The first mask layer including a first hole. The methodincludes implanting a first implant and a second implant, through thefirst mask layer, into the second well region to form a first dopedregion. The first doped region includes a lower portion having the firstconductivity type, and an upper portion stacked on the lower region andhaving the second conductivity type. The method further includesremoving the first mask layer from the first epitaxial layer, forming asecond epitaxial layer of the first conductivity type on the firstepitaxial layer, and forming a third well region in the second epitaxiallayer. The third well region has the second conductivity type. Thefirst, second and third well regions form a continuous well region. Themethod further includes forming a second mask layer over the secondepitaxial layer. The second mask layer includes a second hole. Themethod includes implanting the first implant and the second dopant,through the second mask layer, into the third well region to form asecond doped region such that the first doped region and the seconddoped region are vertically and horizontally offset from each other. Thesecond doped region includes a lower portion having the firstconductivity type, and an upper portion stacked on the lower region andhaving the second conductivity type. The method further includesremoving the second mask layer from the second epitaxial layer.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will now be made, by way of example, to the accompanyingdrawings which show example embodiments of the present application, andin which:

FIGS. 1 a-1 b show an example power semiconductor device consistent withsome embodiments of this disclosure;

FIGS. 2 a-2 b show an example power semiconductor device consistent withsome embodiments of this disclosure;

FIGS. 3 a-3 b show an example power semiconductor device consistent withsome embodiments of this disclosure;

FIGS. 4 a-4 b show an example power semiconductor device consistent withsome embodiments of this disclosure;

FIGS. 5 a-5 e show example methods of manufacturing a powersemiconductor device consistent with some embodiments of thisdisclosure;

FIG. 6 shows other example methods of manufacturing a powersemiconductor device consistent with some embodiments of thisdisclosure;

FIGS. 7 a-7 d shows other example methods of manufacturing a powersemiconductor device consistent with some embodiments of thisdisclosure;

FIGS. 8 a-8 c shows other example methods of manufacturing a powersemiconductor device consistent with some embodiments of thisdisclosure;

FIG. 9 a shows another example power semiconductor device consistentwith some embodiments of this disclosure;

FIG. 9 b shows another example power semiconductor device consistentwith some embodiments of this disclosure;

FIG. 9 c shows another example power semiconductor device consistentwith some embodiments of this disclosure;

FIG. 10 shows another example power semiconductor device consistent withsome embodiments of this disclosure; and

FIGS. 11 a-11 h show example methods of manufacturing a powersemiconductor device consistent with some embodiments of thisdisclosure.

DESCRIPTION OF EXAMPLE EMBODIMENTS

Detailed example embodiments are described below and illustrated in theaccompanying drawings.

Reference is now made to FIG. 1, which shows an example powersemiconductor device 10. Device 10 is an n-type device and includes ap-type semiconductor substrate 102. A gate structure 116 and a fieldinsulating layer 114 are on substrate 102. A gate insulating layer 118is disposed between gate structure 116 and substrate 102. A portion ofgate insulating layer 118 extends to cover a portion of field insulatinglayer 114. Moreover, a p-type body region 106 and an n-type well region104 are respectively disposed in substrate 102 on both sides of gatestructure 116. A p-type contact region 108 and an adjacent n-typecontact region 110 collectively as a source region 111 are disposed inbody region 106, and an n-type contact region as a drain region 112 isdisposed in well region 104.

Moreover, a plurality of doped regions 132, 134, 136, 138 are disposedin well region 104 between source region 111 and drain region 112. Dopedregion 132 includes a p-type lower portion 132 a and an n-type upperportion 132 b stacked on top of lower portion 132 a. Similarly, dopedregions 134, 136, 138 include p-type lower portions 134 a, 136 a, 138 a,and n-type upper portions 134 b, 136 b, 138 b, respectively. It can beappreciated that although four doped regions are shown in FIG. 1, thenumber of the doped regions may be more or less than four according tosome embodiments.

Doped regions 132, 134, 136, 138 are arranged in well region 104 suchthat they are at least vertically and horizontally offset from eachother. For example, doped region 132 is vertically and horizontallyseparated from doped region 134. Moreover, although doped region 134 isvertically and horizontally offset from doped region 136, n-type upperportion 134 b is in contact with p-type lower portion 136 a. Further,depths of doped regions 132, 134, 136, 138 as measured from the surfaceof substrate 102 (the interface between substrate 102 and of fieldinsulating layer 114 as shown in FIG. 1 a) are set in an ascending orderin a direction from source region 111 to drain region 112.

In some embodiments, the depths of doped regions 132, 134, 136, 138 maybe determined by an electric field distribution profile of well region104. FIG. 1 b shows an electric field distribution profile of wellregion 104 of FIG. 1 a before doped regions 132, 134, 136, 138 aredisposed in well region 104. Based on the profile, doped region 132 isarranged deeper in well region 104 where the electric field is stronger,while doped region 138 is arranged adjacent to the surface where theelectric field is weaker.

Moreover, a conductive source electrode 120 is electrically connected top-type contact region 108 and n-type contact region 110. A conductivedrain electrode 124 is electrically connected to n-type contact region112. A conductive gate electrode 122 is electrically connected to gatestructure 116. An interlayer dielectric layer 126 is disposed to coverelectrodes 120, 122, 124.

FIGS. 2-4 show some other embodiments of this disclosure. Legendssimilar to those in FIG. 1 are omitted for brevity. FIGS. 2 b, 3 b, and4 b show different electric field distribution profiles of devicesbefore doped regions 132, 134, 136, 138 are disposed in well region 104in each of devices 11, 12, and 13.

After an electric field distribution profile is determined, dopedregions 132, 134, 136, 138 may be arranged based on the determinedprofile. For example, referring to FIG. 2 which shows an examplesemiconductor device 11, depths of doped regions 132, 134, 136, 138 asmeasured from the surface of substrate 102 are set in a descending orderas the electric field decreases in well region 104 in a direction fromsource region 111 to drain region 112. Legends not mentioned here andsimilar to those in FIG. 1 a are omitted for brevity.

Referring to FIG. 3 which shows another example semiconductor device 12,doped region 134 having the largest depth is arranged between dopedregions 132 and 136, while doped region 138 is arranged adjacent to thesurface of substrate 102 based on the determined profile as shown inFIG. 3 b. As shown in FIGS. 3 a and 3 b, the doped region 134 isarranged deeper in well region 104 where the electric field is stronger,while doped region 138 is arranged adjacent to the surface where theelectric field is weaker.

Referring to FIG. 4 which shows another example semiconductor device 13,doped region 134 having the least depth is arranged between dopedregions 132 and 136, while doped region 138 is arranged to have thelargest depth from the surface of substrate 102 based on the determinedprofile in FIG. 4 b. As shown in FIGS. 4 a and 4 b, the doped region 138is arranged deeper in well region 104 where the electric field isstronger, while doped region 134 is arranged adjacent to the surfacewhere the electric field is weaker.

It can be appreciated that the locations or depths of doped regions arenot limited to the above example embodiments. Further, it can beappreciated that the locations or depths of doped regions may bemodified based on design parameters other than electric fielddistribution profile. Example parameters may be

With the above example structures, it is possible to increase thebreakdown voltage of a power semiconductor device and at the same timeto reduce the ON-resistance. Moreover, because of the inclusion of dopedregions 132, 134, 136, 138 in semiconductor devices 10-13, it ispossible to reduce the overall size of the device, and therefore,increase the number of the device per unit area.

Next, example methods of manufacturing power semiconductor device 10 ofFIG. 1 a will be described with corresponding figures. Referring to FIG.5 a, a p-type semiconductor substrate 102 is prepared for processing.Preparation of substrate 102 may include cleaning or other treatment toprovide a suitable surface for subsequent steps. Substrate 102 isprovided with a sacrificing layer 150 for conducting implantation.Semiconductor substrate 102 may be a silicon substrate, silicon oninsulator (SOI) substrate, SiGe substrate or other suitablesemiconductor substrate. Sacrificing layer 150 may be an oxide, nitride,or oxynitride layer, for example. An implantation protection layer 152,such as a photoresist layer, is provided on sacrificing layer 150.Implantation protection layer 152 is patterned to expose a region wherean implant will be applied. Next, an n-type implant is implanted intosubstrate 102 to form well region 104. A doping concentration of then-type implant for the well region is set to be higher than that ofsubstrate 102, and about, for example, 1e11 to 1e13 atoms/cm² or, insome embodiments, about 1e11 to 5e12 atoms/cm². After n-type implant isimplanted into substrate 102, post-implantation steps, such as annealingand removal of sacrificing layer 150 and implantation protection layer152, may be applied.

Referring to FIG. 5 b, a mask layer 160, such as a hard mask, is formedon substrate 102. Mask layer 160 may include an oxide, nitride, oroxynitride, or other organic material. Mask layer 160 may be formed byphysical or chemical vapor deposition or other suitable coatingprocesses. Mask layer 160 is then patterned to form holes 162 such thatat least one of holes 162 penetrates mask layer 160 to expose a surfaceof substrate 102 at well region 104. Further, a portion of holes 162 ispatterned to form a staircase structure. As shown in FIG. 5 b, the holeshave different depths from an upper surface of mask layer 160.Alternatively, mask layer 160 may be printed on substrate 102 with holes162. In some embodiments, a thin sacrificing layer similar tosacrificing layer 150 shown in FIG. 5 a may be provided to interposebetween mask layer 160 and substrate 102. In some embodiments, beforepatterning mask layer 160 to form holes 162, an electric fielddistribution profile in the well region is determined. The depths andlocations of holes 162 in mask layer 160 may be determined based on thedetermined electric field distribution profile.

Referring to FIG. 5 c, a p-type implant is implanted into well region104, via mask layer 160, to simultaneously form p-type lower portions132 a, 134 a, 136 a, 138 a. The p-type implant may be implanted withsame implantation energy for p-type lower portions 132 a, 134 a, 136 a,138 a. Moreover, an n-type implant is implanted into well region 104,via mask layer 160 to simultaneously form n-type upper portions 132 b,134 b, 136 b, 138 b, respectively stacking on lower portions 132 a, 134a, 136 a, 138 a, so as to form doped regions 132, 134, 136, and 138. Then-type implant may be implanted with same implantation energy to formn-type upper portions 132 b, 134 b, 136 b, 138 b. However, the sequenceof the implantation is not limited. In some embodiments, the n-typeimplant may be implanted into well region 104 before the p-type implant.A doping concentration of the p-type implant for p-type lower portions132 a, 134 a, 136 a, 138 a, or of the n-type implant for n-type upperportions 132 b, 134 b, 136 b, 138 b may be set to be about, for example,1e11 to 1e13 atoms/cm² so that the doping concentrations in dopedregions 132, 134, 136, and 138 are higher than that of well region 104.In some embodiments, p-type lower portions 132 a, 134 a, 136 a, 138 aare doped with a p-type implant at a concentration higher than theconcentration for well region 104, while n-type upper portions 132 b,134 b, 136 b, 138 b are doped with an n-type implant at a concentrationlower than the concentration for well region 104.

Referring to FIG. 5 d, a p-type implant is implanted into substrate 102to form body region 106. Although not shown in FIG. 5 d, another set ofsacrificing layer 150 and implantation protection layer 152 similar tothose in FIG. 5 a may be utilized to form body region 106 during theimplantation. A doping concentration of the p-type implant for the bodyregion is set to be about, for example, 1e11 to 1e14 atoms/cm².

Still referring to FIG. 5 d, after well region 104, body region 106, anddoped regions 132, 134, 136, 138 are formed in substrate 102, aninsulating layer 114 is formed on the surface of substrate 102.Insulating layer 114 may be an oxide, nitride, or oxynitride. Insulatinglayer 114 may be formed by oxidation and/or nitridation of thesubstrate, or deposition of oxide, nitride, and/or oxynitride materialson the substrate. As shown in FIG. 5 d, insulating layer 114 is formedon substrate 102 to expose a surface of substrate 102, well region 104,and body region 106.

Referring again to FIG. 5 d, a gate insulating layer 118 is formed onsubstrate 102 to cover a portion of insulating layer 114, and a surfaceof substrate 102 and body region 106. Gate insulating layer 118 may be,for example, an oxide, nitride, or oxynitride. Moreover, a gatestructure 116 is formed on gate insulating layer 118. Gate structure 116may be of polysilicon, metal, or metal silicide, or other conductivematerial.

Referring to FIG. 5 e, a source region 111 including p-type contactregion 108 and an adjacent n-type contact region 110, and drain region112 having a n-type contact region are respectively formed in bodyregion 106 and well region 104. Source region 111 and drain region 112may be formed by implanting corresponding implants into body region 106and well region 104. Doping concentrations of the source region 111 anddrain region 112 may be set at about, for example, 1e11 to 1e16atoms/cm². In some embodiments, doping concentrations for the source anddrain regions may be set at, for example, about 1e13 to 1e16 atoms/cm²or, in other embodiments, about 1e14 to 1e16 atoms/cm². Thereafter, asource electrode 120 is formed to electrically connect to p-type contactregion 108 and n-type contact region 110. A drain electrode 124 isformed to electrically connect to drain region 112. A gate electrode 122is formed to electrically connect to gate structure 116. Theseelectrodes may be formed sequentially or at the same time. In addition,a material of these electrodes may be selected from polysilicon, metal,or metal silicide, or other conductive materials. In some embodiments,the materials of the electrodes and the gate structure may be the same.An interlayer dielectric layer 126 is deposited on substrate 102 tocover the electrodes. Although not illustrated, multiple layers ofinterconnection may be provided on the substrate in device 10.

As shown in FIG. 5 c, holes 162 provided in mask layer 160 allowsimultaneously formation of p-type lower portions 132 a, 134 a, 136 a,138 a or n-type upper portions 132 b, 134 b, 136 b, 138 b. P-type lowerportions 132 a, 134 a, 136 a, 138 a may be vertically and horizontallyoffset from each other. N-type upper portions 132 b, 134 b, 136 b, 138 bmay be vertically and horizontally offset from each other. In someembodiments, the contour of the holes in mask layer 160 may be modifiedbased on how doped regions 132, 134, 136, 138 are arranged in wellregion 104. For example, as shown in FIG. 6, another mask layer 160having holes 162 may be utilized to form doped regions 132, 134, 136,138 in well region 104. Specifically, an implant going through hole 162that has the largest depth from an upper surface of mask layer 160produces doped region 134 that has the largest depth from the surface ofsubstrate 102. And an implant going through hole 162 that has the leastdepth from the upper surface of mask layer 160 produces doped region 138disposed adjacent to the surface of substrate 102.

While it may be beneficial to form the upper portions or lower portionsof doped regions 132, 134, 136, 138 simultaneously with a single masklayer, formation of the doped regions is not limited to this technique.In some embodiments, more than one mask layer may be employed. Forexample, referring to FIG. 7 a, after substrate 102 is provided withwell region 104, a first mask layer 172 is coated on substrate 102.First mask layer 172 is provided with a hole 173. P-type and n-typeimplants are respectively implanted into well region via hole 173 toform p-type lower portion 138 a and n-type upper portion 138 b,collectively a doped region 138. First mask layer 172 is then removedand a second mask layer 174 is coated on substrate 102 (FIG. 7 b).

Referring to FIG. 7 b, second mask layer 174 is provided with a hole175. P-type and n-type implants are respectively implanted into wellregion via hole 175 to form p-type lower portion 136 a and n-type upperportion 136 b, collectively a doped region 136. Note that because dopedregion 136 is deeper in well region 104 than doped region 138, theimplantation energy for forming doped region 136 may be higher than thatfor forming doped region 138. Second mask layer 174 is then removed anda third mask layer 176 is coated on substrate 102 (FIG. 7 c).

Referring to FIG. 7 c, third mask layer 176 is provided with a hole 177.P-type and n-type implants are respectively implanted into well regionvia hole 177 to form p-type lower portion 134 a and n-type upper portion134 b, collectively a doped region 134. Similarly, the implantationenergy for forming doped region 134 may be higher than that for formingdoped region 136 or 138. Third mask layer 176 is then removed and afourth mask layer 178 is coated on substrate 102 (FIG. 7 d).

Referring to FIG. 7 d, fourth mask layer 178 is provided with a hole179. P-type and n-type implants are respectively implanted into wellregion via hole 179 to form p-type lower portion 132 a and n-type upperportion 132 b, collectively a doped region 132. The above steps may berepeated until all of the doped regions are arranged in the well regionaccording to predetermined criteria.

Another example method to form doped regions with a plurality of masklayers is shown in FIGS. 8 a-8 c. Referring to FIG. 8 a, after substrate102 is provided with well region 104, a first mask layer 180 is coatedon substrate 102. First mask layer 180 is provided with a hole 181.P-type and n-type implants are respectively implanted into well region104 via hole 181 to form p-type lower portion 138 a and n-type upperportion 138 b, collectively a doped region 138. First mask layer 180 isthen removed and a second mask layer 182 is coated on substrate 102(FIG. 8 b).

Referring to FIG. 8 b, second mask layer 182 is provided with two holes183. A p-type implant is implanted into well region 104 via holes 183 toform p-type lower portions 136 a and 132 a, and an n-type implant isimplanted into well region 104 via holes 183 to form n-type upperportions 136 b and 132 b. Thus, a single mask layer may be employed toform two doped regions 132 and 136. Note that because doped regions 132and 136 are deeper in well region 104 than doped region 138, theimplantation energy for forming doped regions 132 and 136 may be higherthan that for forming doped region 138. Second mask layer 182 is thenremoved and a third mask layer 184 is coated on substrate 102 (FIG. 8c).

Referring to FIG. 8 c, third mask layer 184 is provided with a hole 185.P-type and n-type implants are respectively implanted into well regionvia hole 185 to form p-type lower portion 134 a and n-type upper portion134 b, collectively a doped region 134. Similarly, the implantationenergy for forming doped region 134 may be higher than that for formingdoped regions 132, 136, 138.

Consistent with embodiments discussed with FIGS. 1-4, in someembodiments, the above methods to form semiconductor devices mayoptionally include a step of determining an electric field distributionprofile in the well region to determine locations and depths of theholes in the mask layers.

Although the example power semiconductor devices described above aren-type devices, power semiconductor devices consistent with someembodiments can be p-type. The structure of a p-type power semiconductordevice can be the same as those of the n-type power semiconductor deviceas described above, but the conductivity type of the materials in ap-type power semiconductor device is set to be opposite to that of then-type power semiconductor device.

FIG. 9 a depicts another power semiconductor device 90 consistent withembodiments of this disclosure. Device 90 is an n-type device andincludes a p-type substrate 900 and an epitaxial layer 902 disposed onsubstrate 900. A gate structure 916 and a field insulating layer 914 aredisposed on epitaxial layer 902. A gate insulating layer 918 is disposedbetween gate structure 916 and epitaxial layer 902. A portion of gateinsulating layer 918 extends to cover a portion of field insulatinglayer 914.

Moreover, a p-type body region 906 is disposed in epitaxial layer 902.N-type well regions 904 are disposed in both substrate 900 and epitaxiallayer 902. A p-type contact region 908 and an adjacent n-type contactregion 910 collectively constitute a source region 911, which isdisposed in body region 906. An n-type contact region constitutes adrain region 912 and is disposed in well region 904 in epitaxial layer902. A doped region 932 is disposed in well region 904 of substrate 900.Doped region 932 includes a p-type lower portion 932 a and an n-typeupper portion 932 b stacked on top of lower portion 932 a. Further, adoped region 934 is disposed in well region 904 of epitaxial layer 902.Doped region 934 includes a p-type lower portion 934 a and an n-typeupper portion 934 b stacked on top of lower portion 934 a. Doped regions932 and 934 are disposed between source region 911 and drain region 912.It can be appreciated that although one doped region is disposed in eachof substrate 900 and epitaxial layer 902 as shown in FIG. 9 a, each ofsubstrate 900 and epitaxial layer 902 may include more than one dopedregion according to some embodiments. Referring to FIG. 9 b which showsa semiconductor device 91, epitaxial layer 902 includes two dopedregions 934 and 936 separated from each other.

Moreover, a conductive source electrode 920 is electrically connected top-type contact region 908 and n-type contact region 910. A conductivedrain electrode 924 is electrically connected to n-type contact region912. A conductive gate electrode 922 is electrically connected to gatestructure 916. An interlayer dielectric layer 926 is disposed to coverelectrodes 920, 922, 924.

Doped regions 932 and 934 are arranged in well regions 904 such thatthey are at least vertically and horizontally offset from each other. InFIG. 9 a, doped regions 932 and 934 are vertically and horizontallyseparated from each other. However, in some embodiments, althoughvertically and horizontally offset, doped regions 932 and 934 maypartially overlap with each other as shown in FIG. 9 c which shows asemiconductor device 91.

In some embodiments, more than one epitaxial layer may be formed onsubstrate 900 in a power semiconductor device. Each epitaxial layer isprovided with a well region and at least one doped region. Referring toFIG. 10, a power semiconductor device 93 is a n-type device and includesa p-type substrate 900 and two epitaxial layers 902 a and 902 b(collectively epitaxial structure 902) disposed on substrate 900. A gatestructure 916 and a field insulating layer 914 are disposed on epitaxiallayer 902 b. A gate insulating layer 918 is disposed between gatestructure 916 and epitaxial layer 902 b. A portion of gate insulatinglayer 918 extends to cover a portion of field insulating layer 914.Although device 92 is shown to have two epitaxial layers, the number ofepitaxial layers is not limited, and can be more than two.

Still referring to FIG. 10, a p-type body region 906 is disposed inepitaxial layer 902 b. N-type well regions 904 are disposed in bothsubstrate 900 and epitaxial layers 902 a and 902 b so that these wellregions form a continuous well region. A p-type contact region 908 andan adjacent n-type contact region 910 collectively constitute a sourceregion 911, which is disposed in body region 906. An n-type contactregion constitutes a drain region 912 and is disposed in well region 904in epitaxial layer 902 b. A doped region 932 is disposed in well region904 of substrate 900. Doped region 932 includes a p-type lower portion932 a and an n-type upper portion 932 b stacked on top of lower portion932 a. Further, doped regions 934 and 936 are disposed in well regions904 of epitaxial layers 902 a and 902 b, respectively. Doped regions 934includes a p-type lower portion 934 a and an n-type upper portion 934 bstacked on top of lower portion 934 a. Doped regions 936 includes ap-type lower portion 936 a and an n-type upper portion 936 b stacked ontop of lower portion 936 a. Doped regions 932, 934, 936 are disposedbetween source region 911 and drain region 912. It can be appreciatedthat although one doped region is disposed in each of substrate 900 andepitaxial layers 902 a, 902 b as shown in FIG. 10, each of substrate 900and epitaxial layers 902 a, 902 b may include more than one doped regionaccording to some embodiments. Moreover, in some embodiments, dopedregion 934 of epitaxial layer 902 a or doped region 932 of substrate 900may be omitted from FIG. 10.

Moreover, a conductive source electrode 920 is electrically connected top-type contact region 908 and n-type contact region 910. A conductivedrain electrode 924 is electrically connected to n-type contact region912. A conductive gate electrode 922 is electrically connected to gatestructure 916. An interlayer dielectric layer 926 is disposed to coverelectrodes 920, 922, 924.

Doped regions 932, 934, 936 are arranged in well regions 904 such thatthey are at least vertically and horizontally offset from each other. Itshould be noted that well region 904 or doped region 932 in substrate900 as shown in FIG. 10 may be omitted.

Next, example methods of manufacturing devices 92 as shown in FIG. 10will be described with corresponding figures. Referring to FIG. 11 a, ap-type semiconductor substrate 902 is prepared for processing. Substrate900 is provided with a sacrificing layer 150 for conductingimplantation. Semiconductor substrate 900 may be a silicon substrate,silicon on insulator (SOI) substrate, SiGe substrate or other suitablesemiconductor substrate. Sacrificing layer 150 may be an oxide, nitride,or oxynitride layer, for example. An implantation protection layer 152,such as a photoresist layer, is provided on sacrificing layer 150.Implantation protection layer 152 is patterned to expose a region wherean implant will be applied. Next, an n-type implant is implanted intosubstrate 900 to form well region 904. A doping concentration of then-type implant for well region 904 is set to be higher than that ofsubstrate 900, and about, for example, 1e11 to 1e13 atoms/cm² or, insome embodiments, about 1e11 to 5e12 atoms/cm². After n-type implant isimplanted into substrate 900, sacrificing layer 150 and implantationprotection layer 152 are removed from substrate 900.

Referring to FIG. 11 b, a mask layer 200 such as a hard mask is formedon substrate 900. Mask layer 200 may include an oxide, nitride, oroxynitride, or other organic material. Mask layer 200 may be formed byphysical or chemical vapor deposition or other suitable coatingprocesses. Mask layer 200 is then patterned to form a hole 201penetrating mask layer 200 to expose a surface of substrate 900 at wellregion 904. Alternatively, mask layer 200 may be printed on substrate900 with a plurality of holes 201. In some embodiments, a thinsacrificing layer similar to sacrificing layer 150 shown in FIG. 11 amay be provided to interpose between mask layer 200 and substrate 900.

Still referring to FIG. 11 b, a p-type implant is implanted into wellregion 904, via mask layer 200, to form p-type lower portion 932 a.Moreover, an n-type implant is implanted into well region 104, via masklayer 200, to form n-type upper portion 932 b stacking on lower portion932 a, so as to form doped region 932. However, the sequence of theimplantation is not limited. In some embodiments, the n-type implant maybe implanted into well region 104 before the p-type implant. A dopingconcentration of the p-type implant for p-type lower portion 932 a, orof the n-type implant for n-type upper portion 932 b may be set to beabout, for example, 1e11 to 1e13 atoms/cm² so that the dopingconcentration in doped region 932 is higher than that of well region904. In some embodiments, p-type lower portion 932 a is doped with ap-type implant at a concentration higher than the concentration for wellregion 904, while n-type upper portion 932 b is doped with an n-typeimplant at a concentration lower than the concentration for well region904.

Referring to FIG. 11 c, a first p-type epitaxial layer 902 a is grown onsubstrate 900. Epitaxial layer 902 a may include material(s) the same asor different from that of substrate 900. A sacrificing layer 150 andimplantation protection layer 152 similar to those shown in FIG. 11 afor conducting implantation is provided on epitaxial layer 902 a. Ann-type implant is implanted into epitaxial layer 902 a to form wellregion 904 therein. A doping concentration of the n-type implant forwell region 904 is set to be higher than that of epitaxial layer 902 a,and about, for example, 1e11 to 1e13 atoms/cm² or, in some embodiments,about 1e11 to 5e12 atoms/cm². After n-type implant is implanted intoepitaxial layer 902 a, sacrificing layer 150 and implantation protectionlayer 152 are removed from epitaxial layer 902 a.

Referring to FIG. 11 d, another mask layer 202 such as a hard mask isformed on epitaxial layer 902 a. Mask layer 202 is patterned to form ahole 203 penetrating mask layer 202 to expose a surface of epitaxiallayer 902 a at well region 904. Alternatively, mask layer 202 may beprinted on epitaxial layer 902 a with holes 203. In some embodiments, athin sacrificing layer similar to sacrificing layer 150 shown in FIG. 11a may be provided to interpose between mask layer 202 and epitaxiallayer 902 a.

Still referring to FIG. 11 d, a p-type implant and an n-type implant arerespectively implanted into well region 904 of epitaxial layer 902 a,via mask layer 202, to form p-type lower portion 934 a and n-type upperportion 934 b on lower portion 934 a, so as to form doped region 934. Adoping concentration of the p-type implant for p-type lower portion 934a, or of the n-type implant for n-type upper portion 934 b may be set tobe about, for example, 1e11 to 1e13 atoms/cm² so that the dopingconcentration in doped region 934 is higher than that of well region 904of epitaxial layer 902 a. In some embodiments, p-type lower portion 934a is doped with a p-type implant at a concentration higher than theconcentration for well region 904, while n-type upper portion 934 b isdoped with an n-type implant at a concentration lower than theconcentration for well region 904.

Referring to FIG. 11 e, a second p-type epitaxial layer 902 b is grownon epitaxial layer 902 a. A sacrificing layer 150 and implantationprotection layer 152 similar to those shown in FIG. 11 a for conductingimplantation is provided on epitaxial layer 902 b. An n-type implant isimplanted into epitaxial layer 902 b to form well region 904 therein. Adoping concentration of the n-type implant for well region 904 is set tobe higher than that of epitaxial layer 902 a, and about, for example,1e11 to 1e13 atoms/cm² or, in some embodiments, about 1e11 to 5e12atoms/cm². After n-type implant is implanted into epitaxial layer 902 b,sacrificing layer 150 and implantation protection layer 152 are removedfrom epitaxial layer 902 b.

Referring to FIG. 11 f, a mask layer 204 such as a hard mask is formedon epitaxial layer 902 b. Mask layer 204 is patterned to form a hole 205penetrating mask layer 204 to expose a surface of epitaxial layer 902 bat well region 904. Alternatively, mask layer 204 may be printed onepitaxial layer 902 b with holes 205. In some embodiments, a thinsacrificing layer similar to sacrificing layer 150 shown in FIG. 11 amay be provided to interpose between mask layer 204 and epitaxial layer902 b.

Still referring to FIG. 11 f, a p-type implant and an n-type implant arerespectively implanted into well region 904 of epitaxial layer 902 b,via mask layer 204, to form p-type lower portion 936 a and n-type upperportion 936 b on lower portion 936 a, so as to form doped region 936. Adoping concentration of the p-type implant for p-type lower portion 936a, or of the n-type implant for n-type upper portion 936 b may be set tobe about, for example, 1e11 to 1e13 atoms/cm² so that the dopingconcentration in doped region 936 is higher than that of well region 904of epitaxial layer 902 b. In some embodiments, p-type lower portion 936a is doped with a p-type implant at a concentration higher than theconcentration for well region 904, while n-type upper portion 936 b isdoped with an n-type implant at a concentration lower than theconcentration for well region 904.

Referring to FIG. 11 g, a p-type implant is implanted into epitaxiallayer 902 b to form body region 906. Although not shown in FIG. 11 g,another set of sacrificing layer 150 and implantation protection layer152 similar to those in FIG. 11 a may be utilized to form body region906. A doping concentration of the p-type implant for the body region isset to be about, for example, 1e11 to 1e14 atoms/cm².

Still referring to FIG. 11 g, after well region 904, body region 906,and doped regions 932, 934, 936 are formed, an insulating layer 914 isformed on the surface of epitaxial layer 902 b. Insulating layer 914 maybe an oxide, nitride, or oxynitride. Insulating layer 914 may be formedby oxidation and/or nitridation of epitaxial layer 902 b, or depositionof oxide, nitride, and/or oxynitride materials on epitaxial layer 902 b.As shown in FIG. 11 g, insulating layer 914 is formed on epitaxial layer902 b to expose well region 904, body region 906, and a surface ofepitaxial layer 902 b adjacent to body region 906.

Referring again to FIG. 11 g, a gate insulating layer 918 is formed onepitaxial layer 902 b to cover a portion of insulating layer 914, and asurface of epitaxial layer 902 b and body region 906. Gate insulatinglayer 918 may be, for example, an oxide, nitride, or oxynitride.Moreover, a gate structure 916 is formed on gate insulating layer 918.Gate structure 916 may be of polysilicon, metal, or metal silicide, orother conductive material.

Referring to FIG. 11 h, a source region 911 including a p-type contactregion 908 and an adjacent n-type contact region 910, and drain region912 are respectively formed in body region 906 and well region 904.Source region 911 and drain region 912 may be formed by implantingcorresponding implants into body region 906 and well region 904. Dopingconcentrations of source region 911 and drain region 912 may be, forexample, about 1e11 to 1e16 atoms/cm². In some embodiments, dopingconcentrations for the source and drain regions may be set at, forexample, about 1e13 to 1e16 atoms/cm² or, in other embodiments, about1e14 to 1e16 atoms/cm². Thereafter, a conductive source electrode 920 isformed to electrically connect to p-type contact region 908 and n-typecontact region 910. A conductive drain electrode 924 is formed toelectrically connect to n-type contact region 912. A conductive gateelectrode 922 is formed to electrically connect to gate structure 916.These electrodes may be formed sequentially or at the same time. Inaddition, a material of these electrodes may be selected frompolysilicon, metal, or metal silicide, or other conductive materials. Insome embodiments, the materials of the electrodes and the gate structuremay be the same. An interlayer dielectric layer 926 is deposited onepitaxial layer 902 b to cover the electrodes. Although not illustrated,multiple layers of interconnection may be provided on the electrodes inthe power semiconductor device.

Although the example power semiconductor devices described above inFIGS. 9-11 are n-type devices, power semiconductor devices consistentwith some embodiments can be p-type. The structure of a p-type powersemiconductor device can be the same as those of the n-type powersemiconductor device as described above, but the conductivity type ofthe materials in a p-type power semiconductor device is set to beopposite to that of the n-type power semiconductor device.

Certain adaptations and modifications of the described embodiments canbe made. Therefore, the above discussed embodiments are considered to beillustrative and not restrictive.

What is claimed is:
 1. A semiconductor device comprising: a substratehaving a first conductivity type; a drain region, a source region, and awell region disposed in the substrate, the well region being disposedbetween the drain region and the source region and having a secondconductivity type opposite to the first conductivity type; and aplurality of doped regions disposed in the well region, the dopedregions being vertically and horizontally offset from each other, eachof the doped regions comprising a lower portion having the firstconductivity type, and an upper portion stacked on the lower region andhaving the second conductivity type.
 2. The semiconductor deviceaccording to claim 1, wherein depths of the doped regions from a surfaceof the substrate are set in an ascending or descending order in adirection from the source region to the drain region.
 3. Thesemiconductor device according to claim 1, wherein depths of the dopedregions from a surface of the substrate are set such that one of thedoped regions having the largest depth is disposed between two adjacentdoped regions.
 4. The semiconductor device according to claim 1, whereindepths of the doped regions from a surface of the substrate are set suchthat one of the doped regions having the least depth is disposed betweentwo adjacent doped regions.
 5. The semiconductor device according toclaim 1, further comprising: a body region of the first conductivitytype disposed under the source region; an insulating layer disposedabove the well region, the insulating layer connected to the drainregion and spaced apart from the source region; a gate insulating layerconnected to the insulating layer and extended to cover a portion of thebody region; and a gate disposed on the insulating layer and the gateinsulating layer.
 6. The semiconductor device according to claim 1,wherein: the well region is doped with a first doping concentration, thelower portion is doped with a second doping concentration, and the upperportion is doped with a third doping concentration; and each of thesecond doping concentration and third doping concentration is higherthan the first doping concentration.
 7. The semiconductor deviceaccording to claim 1, wherein: the well region is doped with a firstdoping concentration, the lower portion is doped with a second dopingconcentration, and the upper portion is doped with a third dopingconcentration; and the second doping concentration is higher than thefirst doping concentration, and the third doping concentration is lowerthan the first doping concentration.
 8. The semiconductor deviceaccording to claim 6, wherein the first doping concentration is about1e11 to 1e13 atoms/cm².
 9. The semiconductor device according to claim7, wherein the first doping concentration is about 1e11 to 1e13atoms/cm².
 10. The semiconductor device according to claim 1, whereinthe first conductivity type is p-type and the second conductivity typeis n-type.
 11. The semiconductor device according to claim 1, whereinthe first conductivity type is n-type and the second conductivity typeis p-type.
 12. A semiconductor device comprising: a substrate having afirst conductivity type; an epitaxial structure having the firstconductivity type disposed on the substrate; a drain region and a sourceregion disposed in the epitaxial structure; a well region interposedbetween the drain region and the source region, the well region beingdisposed in the substrate and the epitaxial structure, the well regionhaving a second conductivity type opposite to the first conductivitytype; a first doped region disposed in the well region of the substrate;and a second doped region disposed in the well region of the epitaxialstructure; the first doped region and the second doped region beingvertically and horizontally offset from each other; each of the dopedregions comprising a lower portion having the first conductivity type,and an upper portion stacked on the lower region and having the secondconductivity type.
 13. The semiconductor device according to claim 12,wherein: the epitaxial structure is composed of a single epitaxiallayer.
 14. The semiconductor device according to claim 12, wherein: theepitaxial structure is composed of a plurality of epitaxial layers; andthe second doped region is disposed in the uppermost layer of theepitaxial layers.
 15. The semiconductor device according to claim 14,wherein: each of the epitaxial layers includes at least a doped region;and the doped regions are vertically and horizontally offset from eachother.
 16. The semiconductor device according to claim 12, whereindepths of the doped regions from a surface of the substrate are set inan ascending or descending order in a direction from the source regionto the drain region.
 17. The semiconductor device according to claim 12,wherein depths of the doped regions from a surface of the substrate areset such that one of the doped regions having the largest depth isdisposed between two adjacent doped regions.
 18. The semiconductordevice according to claim 12, wherein depths of the doped regions from asurface of the substrate are set such that one of the doped regionshaving the least depth is disposed between two adjacent doped regions.19. The semiconductor device according to claim 12, further comprising:a body region of the first conductivity type disposed under the sourceregion; an insulating layer disposed above the well region, theinsulating layer connected to the drain region and spaced apart from thesource region; a gate insulating layer connected to the insulating layerand extended to cover a portion of the body region; and a gate disposedon the insulating layer and the gate insulating layer.
 20. Thesemiconductor device according to claim 12, wherein: the well region isdoped with a first doping concentration, the lower portion is doped witha second doping concentration, and the upper portion is doped with athird doping concentration; and each of the second doping concentrationand third doping concentration is higher than the first dopingconcentration.
 21. The semiconductor device according to claim 12,wherein: the well region is doped with a first doping concentration, thelower portion is doped with a second doping concentration, and the upperportion is doped with a third doping concentration; and the seconddoping concentration is higher than the first doping concentration, andthe third doping concentration is lower than the first dopingconcentration.
 22. The semiconductor device according to claim 20,wherein the first doping concentration is about 1e11 to 1e13 atoms/cm².23. The semiconductor device according to claim 21, wherein the firstdoping concentration is about 1e11 to 1e13 atoms/cm².
 24. Thesemiconductor device according to claim 12, wherein the firstconductivity type is p-type and the second conductivity type is n-type.25. The semiconductor device according to claim 12, wherein the firstconductivity type is n-type and the second conductivity type is p-type.26. A semiconductor device comprising: a substrate having a firstconductivity type; a plurality of epitaxial layers having the firstconductivity type and disposed on the substrate; a drain region and asource region disposed in the uppermost epitaxial layer; a well regioninterposed between the drain region and the source region, the wellregion being disposed in the substrate and the epitaxial layers, thewell region having a second conductivity type opposite to the firstconductivity type; and a plurality of doped regions disposed in theepitaxial layers, at least two of the doped regions being vertically andhorizontally offset from each other; each of the doped regionscomprising a lower portion having the first conductivity type, and anupper portion stacked on the lower region and having the secondconductivity type.
 27. The semiconductor device according to claim 26,wherein: each of the epitaxial layers includes a doped region, and thedoped regions are vertically and horizontally offset from each other.28. The semiconductor device according to claim 26, wherein: at leastone of the epitaxial layers includes a plurality of doped regions; andthe doped regions of the at least one of the epitaxial layers arehorizontally separated from each other and disposed at a substantiallysame vertical level in the at least one of the epitaxial layers.
 29. Thesemiconductor device according to claim 26, wherein depths of the dopedregions from a surface of the substrate are set in an ascending ordescending order in a direction from the source region to the drainregion.
 30. The semiconductor device according to claim 26, whereindepths of the doped regions from a surface of the substrate are set suchthat one of the doped regions having the largest depth is disposedbetween two adjacent doped regions.
 31. The semiconductor deviceaccording to claim 26, wherein depths of the doped regions from asurface of the substrate are set such that one of the doped regionshaving the least depth is disposed between two adjacent doped regions.32. The semiconductor device according to claim 26, further comprising:a body region of the first conductivity type disposed under the sourceregion; an insulating layer disposed above the well region, theinsulating layer connected to the drain region and spaced apart from thesource region; a gate insulating layer connected to the insulating layerand extended to cover a portion of the body region; and a gate disposedon the insulating layer and the gate insulating layer.
 33. Thesemiconductor device according to claim 26, wherein: the well region isdoped with a first doping concentration, the lower portion is doped witha second doping concentration, and the upper portion is doped with athird doping concentration; and each of the second doping concentrationand third doping concentration is higher than the first dopingconcentration.
 34. The semiconductor device according to claim 26,wherein: the well region is doped with a first doping concentration, thelower portion is doped with a second doping concentration, and the upperportion is doped with a third doping concentration; and the seconddoping concentration is higher than the first doping concentration, andthe third doping concentration is lower than the first dopingconcentration.
 35. The semiconductor device according to claim 33,wherein the first doping concentration is about 1e11 to 1e13 atoms/cm².36. The semiconductor device according to claim 34, wherein the firstdoping concentration is about 1e11 to 1e13 atoms/cm².
 37. Thesemiconductor device according to claim 26, wherein the firstconductivity type is p-type and the second conductivity type is n-type.38. The semiconductor device according to claim 26, wherein the firstconductivity type is n-type and the second conductivity type is p-type.39. A method of manufacturing a semiconductor device, comprising:preparing a substrate of a first conductivity type; forming a wellregion in the substrate, the well region having a second conductivitytype opposite to the first conductivity type; forming a mask layer overthe substrate, the mask layer including a plurality of holes, the holeshaving different depths from an upper surface of the mask layer; andimplanting a first implant through the mask layer and into the wellregion to form a plurality of first doped portions, at least two of thefirst doped portions being vertically and horizontally offset from eachother, the first doped portions having the first conductivity type; andimplanting a second implant through the mask layer and into the wellregion to form a plurality of second doped portions, at least two of thesecond doped portions being vertically and horizontally offset from eachother, the second doped portions stacked on the first doped portions andhaving the second conductivity type.
 40. The method according to claim39, wherein the forming of the mask layer comprises: coating a materiallayer on the substrate; and patterning the material layer such that atleast one of the holes penetrates the material layer.
 41. The methodaccording to claim 39, wherein the first doped portions or the seconddoped portions are formed simultaneously.
 42. The method according toclaim 39, wherein the first doped portions or the second doped portionsare formed using a constant implantation energy.
 43. The methodaccording to claim 39, further comprising: determining an electric fielddistribution profile in the well region; and forming the holes withdepths of the holes based on the determined profile.
 44. The methodaccording to claim 39, further comprising: forming a body region of thefirst conductivity type in the substrate; forming an insulating layerabove the well region; forming a gate insulating layer to connect to theinsulating layer and cover a portion of the body region; forming a gateon the insulating layer and the gate insulating layer; forming a drainregion in the well region; and forming a source region in the bodyregion, the source region and the drain region being disposed ondifferent sides of the insulating layer.
 45. The method according toclaim 39, further comprising: doping the well region with a first dopingconcentration; doping the first doped portions with a second dopingconcentration; and doping the second doped portions with a third dopingconcentration, wherein each of the second doping concentration and thirddoping concentration is higher than the first doping concentration. 46.The method according to claim 39, further comprising: doping the wellregion with a first doping concentration; doping the first dopedportions with a second doping concentration; and doping the second dopedportions with a third doping concentration, wherein the second dopingconcentration is higher than the first doping concentration, and thethird doping concentration is lower than the first doping concentration.47. The method according to claim 39, wherein the first conductivitytype is p-type and the second conductivity type is n-type.
 48. Themethod according to claim 39, wherein the first conductivity type isn-type and the second conductivity type is p-type.
 49. A method ofmanufacturing a semiconductor device, comprising: preparing a substrateof a first conductivity type; forming a well region in the substrate,the well region having a second conductivity type opposite to the firstconductivity type; forming a first mask layer over the substrate, thefirst mask layer including a first hole; implanting a first implant anda second implant through the first mask layer and into the well regionto form a first doped region, the first doped region comprising a lowerportion having the first conductivity type, and an upper portion stackedon the lower region and having the second conductivity type; removingthe first mask layer from the substrate; forming a second mask layerover the substrate, the second mask layer including a second hole;implanting the first implant and the second dopant through the secondmask layer and into the well region to form a second doped region, suchthat the first doped region and the second doped region are verticallyand horizontally offset from each other, the second doped regioncomprising a lower portion having the first conductivity type and anupper portion stacked on the lower region and having the secondconductivity type; and removing the second mask layer from thesubstrate.
 50. The method according to claim 49, wherein the first masklayer or the second mask layer includes more than one hole.
 51. Themethod according to claim 49, wherein energies for implanting the firstdopant to form the first doped region and the second doped region aredifferent.
 52. The method according to claim 49, further comprising:determining an electric field distribution profile in the well region;and determining locations of the first hole and the second hole based onthe determined profile.
 53. The method according to claim 49, furthercomprising: forming a body region of the first conductivity type in thesubstrate; forming an insulating layer above the well region; forming agate insulating layer to connect to the insulating layer and cover aportion of the body region; forming a gate on the insulating layer andthe gate insulating layer; forming a drain region in the well region;and forming a source region in the body region, the source region andthe drain region being disposed on different sides of the insulatinglayer.
 54. The method according to claim 49, further comprising: dopingthe well region with a first doping concentration; doping the lowerportion of the first doped region with a second doping concentration;doping the upper portion of the first doped region with a third dopingconcentration; doping the lower portion of the second doped region witha fourth doping concentration; and doping the upper portion of thesecond doped region with a fifth doping concentration, wherein each ofthe second, third, four, and fifth doping concentrations is higher thanthe first doping concentration.
 55. The method according to claim 49,further comprising: doping the well region with a first dopingconcentration; doping the lower portion of the first doped region with asecond doping concentration; doping the upper portion of the first dopedregion with a third doping concentration; doping the lower portion ofthe second doped region with a fourth doping concentration; and dopingthe upper portion of the second doped region with a fifth dopingconcentration, wherein the second and fourth doping concentrations arehigher than the first doping concentration, and the third and fifthdoping concentrations are lower than the first doping concentration. 56.The method according to claim 49, wherein the first conductivity type isp-type and the second conductivity type is n-type.
 57. The methodaccording to claim 49, wherein the first conductivity type is n-type andthe second conductivity type is p-type.
 58. A method of manufacturing asemiconductor device, comprising: preparing a substrate of a firstconductivity type; forming a first well region in a substrate, the firstwell region having a second conductivity type opposite to the firstconductivity type; forming a first epitaxial layer of the firstconductivity type on the substrate; forming a second well region in thefirst epitaxial layer, the second well region having the secondconductivity type; forming a first mask layer over the first epitaxiallayer, the first mask layer including a first hole; implanting a firstimplant and a second implant through the first mask layer and into thesecond well region to form a first doped region, the first doped regioncomprising a lower portion having the first conductivity type and anupper portion stacked on the lower region and having the secondconductivity type; removing the first mask layer from the firstepitaxial layer; forming a second epitaxial layer of the firstconductivity type on the first epitaxial layer; forming a third wellregion in the second epitaxial layer, the third well region having thesecond conductivity type, the first, second, and third well regionsforming a continuous well region; forming a second mask layer over thesecond epitaxial layer, the second mask layer including a second hole;implanting the first implant and the second dopant through the secondmask layer and into the third well region to form a second doped regionsuch that the first doped region and the second doped region arevertically and horizontally offset from each other, the second dopedregion comprising a lower portion having the first conductivity type andan upper portion stacked on the lower region and having the secondconductivity type; and removing the second mask layer from the secondepitaxial layer.
 59. The method according to claim 58, wherein the firstmask layer or the second mask layer includes more than one hole.
 60. Themethod according to claim 58, wherein energy for implanting the firstdopant to form the first doped region and the second doped region issubstantially constant.
 61. The method according to claim 58, furthercomprising: determining an electric field distribution profile in thewell region; and determining locations of the first hole and the secondhole based on the determined profile.
 62. The method according to claim58, further comprising: forming a body region of the first conductivitytype in the second epitaxial layer; forming an insulating layer abovethe third well region; forming a gate insulating layer to connect to theinsulating layer and cover a portion of the body region; forming a gateon the insulating layer and the gate insulating layer; forming a drainregion in the third well region; and forming a source region in the bodyregion, the source region and the drain region being disposed ondifferent sides of the insulating layer.
 63. The method according toclaim 58, further comprising: doping the well region with a first dopingconcentration; doping the lower portion of the first doped region with asecond doping concentration; doping the upper portion of the first dopedregion with a third doping concentration; doping the lower portion ofthe second doped region with a fourth doping concentration; and dopingthe upper portion of the second doped region with a fifth dopingconcentration, wherein each of the second, third, four, and fifth dopingconcentrations is higher than the first doping concentration.
 64. Themethod according to claim 58, further comprising: doping the well regionwith a first doping concentration; doping the lower portion of the firstdoped region with a second doping concentration; doping the upperportion of the first doped region with a third doping concentration;doping the lower portion of the second doped region with a fourth dopingconcentration; and doping the upper portion of the second doped regionwith a fifth doping concentration, wherein the second and fourth dopingconcentrations are higher than the first doping concentration, and thethird and fifth doping concentrations are lower than the first dopingconcentration.
 65. The method according to claim 58, wherein the firstconductivity type is p-type and the second conductivity type is n-type.66. The method according to claim 58, wherein the first conductivitytype is n-type and the second conductivity type is p-type.